Thermally insulated composite frame members for curtain walls, window frames and the like are well known in the art. Typically, such a frame member consists of two elongated metal sections (usually anodized aluminum) joined by a connector of insulating plastic material. In most conventional applications, the connector must be bonded to the outer sections to provide structural integrity of the composite member. When the adhesive bonds between this connector and each metal section are solely responsible for the structural integrity of the composite member, an insulating plastic which adheres to the metal sections, such as polyurethane, must be used. While the adhesion of polyurethane provides good initial shear strength, thermal cycling, i.e. expansion and contraction resulting from heating and cooling, will destroy polyurethane's ability to resist shear. Also, insulating plastics such as polyvinyl chloride (PVC) or acrylonitrile-butadiene-styrene (ABS) cannot be employed in such a composite member because they may not adhere to anodized aluminum to any appreciable degree.
Accordingly, it is desirable to provide a thermally insulated frame member whose structural integrity does not depend solely upon adhsive bonding between the connector and the aluminum elements, thereby permitting the utilization of non-adhering insulating plastics.
Efforts have been made to provide a thermally insulated composite frame member wherein the plastic connector is mechanically interlocked with the outer aluminum elements. One such example is disclosed in U.S. Pat. No. 3,204,324, wherein the extruded aluminum elements are provided with a plurality of longitudinal projections protruding interiorly of the channels in which the insulating connector is formed. These longitudinal projections extend into the bulk of the insulating connector and provide a mechanical interlock which serves to prevent the aluminum elements from becoming laterally disengaged from the connector in response to tensile force. However, these longitudinal projections do not prevent transverse slippage of the aluminum elements in response to shearing forces, a problem which is aggravated when the plastic connector is exposed to temperature changes and rain or other moisture.
Accordingly, there is a need to provide a thermally insulated frame member wherein the plastic connector is mechanically interlocked with the outer aluminum elements to prevent not only lateral but also transverse slippage of the aluminum elements with respect to the connector.
Conventional thermally insulated members are typically manufactured by the "pour/debridge" method. A unitary elongated aluminum member initially having an interconnecting bar or "bridge" between its inner and outer elements is provided. The bridge forms the bottom wall of an open groove into which is poured a quantity of thermally insulating plastic resin in a fluid condition. When the plastic resin cures into a solid or rigid state and the bridge is removed, the resin forms a connector between the inner and outer elements. When the bridge is removed, the two metal elements are separated but remain joined together by the insulating plastic connector. Thus, a composite structure is formed in which the two aluminum elements are thermally insulated from one another by the plastic thermal-break material.
As discussed above, it is desirable to provide a mechanical interlock to prevent the aluminum elements from being displaced with respect to the insulating connector, whereby the structural integrity of the composite member is not wholly dependent upon adhesive bonding between the plastic connector and the aluminum elements. Longitudinal projections protruding interiorly of the groove into which the plastic insulating material is added, such as those in the aforementioned U.S. Pat. No. 3,204,324, can readily be formed as part of the extrusion process of the anodized aluminum member. Such longitudinal projections extending into the bulk of the plastic connector will prevent the aluminum elements from becoming laterally displaced in response to tensile forces exerted on the outer elements. However, extruded products are essentially linear in character, in the sense that shaping is confined to the cross section only. Thus, while longitudinal projections are easily formed as part of the extrusion process, lateral projections, as would be necessary to mechanically prevent transverse slippage of the aluminum elements with respect to the connector in response to shear forces, cannot be extruded. Accordingly, there is a need to provide a process for manufacturing composite architectural frame members including lateral as well as longitudinal projections protruding interiorly of the groove into which the liquid-state plastic insulating material is poured during the pour/debridge process.